Increasing concerns about rising oil prices are creating an increased interest in the development of economical and convenient alternative energy sources. For example, alternative energy sources may be derived by pelletizing and/or briquetting mixtures of binders and combustible materials, including coal, char, torrefied wood, and other combustible biomass feedstocks. Existing forms of composite combustible materials and binders, however, often lack the desired properties (i.e., water repellence and strength) and are costly.
For example, several practitioners have utilized bio-oils to produce adhesives for woods and other materials. Bio-oil generally is produced by fast pyrolysis of small biomass particles (i.e., lignocellulosic biomass materials) at 400 to 650° C. in the absence of oxygen. The yield of bio-oil is relatively high, at 60 to 80% dry weight basis. Although the chemical properties of bio-oils vary with the type of biomass feedstock, woody biomass feedstocks typically produce a bio-oil with a mixture of 30% water, 30% phenolics, 20% aldehydes and ketones, 15% alcohols and 10% miscellaneous compounds. In addition, bio-oils can contain up to 45% oxygen and may be highly reactive in combination with certain compounds. Not wishing to be bound by any theory, it is believed that the bio-oil's high phenolics content (about 30%) makes it particularly suitable for use as a substitute for existing commercial phenol-containing synthetic binders produced from fossil sources (i.e., just like the presence of phenols in synthetic binders derived from petroleum, the presence of phenols in the bio-oil imparts a degree of water repellence in any bio-oil containing binders).
In addition to bio-oils, hydrolyzed proteins previously have been used to produce adhesives or binders. The hydrolyzed proteins generally are mixed with phenol-containing compounds and/or resins and are cross-linked with a cross-linking agent to obtain the desired properties. For example, U.S. Pat. No. 7,282,117 discloses an adhesive prepared from vegetable protein hydrolyzates combined with phenol formaldehyde resin and/or isocyanate resin. U.S. Patent Publication No. 2005/0272892 discloses an adhesive for structural composite wood panels, such as oriented strand board, particle board and plywood prepared from a soybean hydrolyzate and the familiar cross-linking agent, formaldehyde. U.S. Pat. No. 3,454,508 describes the cross-linking of alkali lignin with a polymethylol phenol combined with formaldehyde to allow a reduction of up to 80% of the required laminating resin. U.S. Pat. No. 4,113,675 discloses the development of a highly cross-linkable methyloated kraft lignin resin produced by combining a premethylolated kraft lignin with a phenolic cross-linking agent (e.g., formaldehyde). These references all suffer from similar disadvantages by continuing to utilize petroleum-based phenols and cross-linking agents (e.g., formaldehyde) to impart improved adhesive and cross-linking properties to the lignin-substituted formulas.